APPROACH FOR MANUFACTURING EFFICIENT MESOPOROUS NANO-COMPOSITE POSITIVE ELECTRODE LiMn1-XFeXPO4 MATERIALS

ABSTRACT

A mesoporous nano-composite LiMn 1-x Fe x PO 4  (0≦x≦1) particle that has a uniform carbon coating on the surface of the particle. Also disclosed is a mesoporous nano-composite LiMn 1-x Fe x PO 4 particle prepared by a process including steps: (i) providing a mixture of a soft-template compound, a lithium ion-containing compound, an iron ion-containing compound, a manganese ion-containing compound, and a phosphate ion-containing compound in a solvent; (2) removing the solvent to obtain a LiMn 1-x Fe x PO 4  precursor; and (3) calcining the precursor followed by milling and annealing to obtain the LiMn 1-x Fe x PO 4 particle.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of U.S. application Ser. No.14/128,433, filed on Dec. 20, 2013, which is a National Stage ofInternational Application No. PCT/SG2012/000228 filed on Jun. 27, 2012,which claims the benefit of U.S. Provisional Application No. 61/501,346filed on Jun. 27, 2011. The contents of all prior applications arehereby incorporated by reference in their entirety.

BACKGROUND

Lithium ion batteries are among the most effective energy storagesystems. They have been used in many electronic devices and are expectedto play prominent roles in the next generation hybrid and plug-in-hybridelectric vehicles. Essential to the performance of these batteries areactive electrode materials capable of reversibly exchanging lithiumions, especially positive electrode materials. LiMn_(1-x)Fe_(x)PO₄(0≦x≦1) particles are promising cathode materials that offer high energydensity and high power density. See Padhi et al., Journal of theElectrochemical Society, 144, 1188-94 (1997); Saravanan et al., Energy &Environmental Science, 3, 457-64 (2010); and Drezen et al., Journal ofPower Sources, 174, 949-53 (2007).

The performance of LiMn_(1-x)Fe_(x)PO₄ particles is largely affected bytheir conductivities and their sizes. See Drezen et al., Journal ofPower Sources, 174, (2), 949-953 (2007); and Doan et al., AdvancedPowder Technology, 21, 187-96 (2010). Several processes have beendeveloped to prepare LiMn_(1-x)Fe_(x)PO₄ particles. For example, solidstate reactions/ball milling processes have been used to prepareLiMn_(1-x)Fe_(x)PO₄ particles in reasonable yields. See Martha et al.,Angewandte Chemie International Edition, 48, 8559-63 (2009). However,these reactions consume a significant amount of energy due to their longcalcination time and high calcination temperature, making themuneconomical in mass production.

There is a need to develop a process that is suitable for massproduction of efficient LiMn_(1-x)Fe_(x)PO₄ materials, in particular,mesoporous nano-composite particles.

SUMMARY

This disclosure is based on the discovery of a process that is suitablefor mass production of high performance mesoporous nano-compositeLiMn_(1-x)Fe_(x)PO₄ particles (0≦x≦1, e.g., x=0, 0.2, 0.5 and 0.8).

Accordingly, one aspect of this disclosure relates to a process ofpreparing mesoporous nano-composite LiMn_(1-x)Fe_(x)PO₄. The processincludes the steps of (a) providing a solvent containing a soft-templatecompound, a lithium ion-containing compound, an iron ion-containingcompound, a manganese ion-containing compound, and a phosphateion-containing compound; (b) removing the solvent to obtain aLiMn_(1-x)Fe_(x)PO₄ precursor; (c) calcining the LiMn_(1-x)Fe_(x)PO₄precursor to obtain crystalline LiMn_(1-x)Fe_(x)PO₄ grains; (d) millingthe crystalline LiMn_(1-x)Fe_(x)PO₄ grains in the presence of conductivecarbon to obtain nanostructured LiMn_(1-x)Fe_(x)PO₄/C particles; and (e)annealing the nanostructured LiMn_(1-x)Fe_(x)PO₄/C particles to obtainmesoporous nano-composite LiMn_(1-x)Fe_(x)PO₄/C particles.

In step (a), the solvent can be a mixture of ethanol and water, in whichthe weight ratio of is ethanol to water is 1:1 to 6:1 (e.g., 5:1); thesoft-template compound can be dodecyltrimethyl-ammonium bromide,(1-hexadecyl)trimethylammonium bromide, octadecyl-trimethylammoniumbromide, tetradecyltrimethylammonium bromide, decyltrimethylammoniumbromide, octyl-trimethylammonium bromide, or pluronic F-127 (e.g,(1-hexadecyl)trimethyl-ammonium bromide and dodecyltrimethylammoniumbromide); the lithium ion-containing compound can be lithium dihydrogenphosphate, lithium acetate, lithium carbonate, lithium hydroxide, orlithium nitrate (e.g., lithium dihydrogen phosphate); the ironion-containing compound can be iron (II) acetate, iron (III) nitrate,iron (III) acetylacetonate, iron (III) chloride, or iron (II) oxalate(e.g., iron (II) acetate); the manganese ion-containing compound can bemanganese (II) acetate, manganese (III) nitrate, manganese (III)acetylacetonate, manganese (III) chloride, or manganese (II) oxalate(e.g., manganese (II) acetate); and the phosphate ion-containingcompound can be lithium dihydrogen phosphate, ammonium dihydrogenphosphate, or phosphoric acid (e.g., lithium dihydrogen phosphate). Theamounts of the lithium ion-containing compound, the ferrousion-containing compound, the manganese ion-containing compound, and thephosphate ion-containing compound are in stoichiometric proportion(e.g., 1:(1-x):x:1 by mole). The weight ratio of the soft-templatecompound to the lithium ion-containing compound is 1:1 to 10:1.

The LiMn_(1-x)Fe_(x)PO₄ precursor obtained in step (b) can be calcinedin step (c) at 550 to 750° C. for 2 to 12 hours, e.g., at 600 to 700° C.for 3 to 6 hours, to afford crystalline LiMn_(1-x)Fe_(x)PO₄ grains.

In step (d), the crystalline LiMn_(1-x)Fe_(x)PO₄ grains can be ballmilled to obtain nanostructured LiMn_(1-x)Fe_(x)PO₄/C particles at 300to 600 rpm in the presence of conductive carbon for 2 to 24 hours, e.g.,at 300 to 500 rpm for 2 to 6 hours.

In step (e), the nanostructured LiMn_(1-x)Fe_(x)PO₄ particles can beannealed to yield mesoporous nano-composite LiMn_(1-x)Fe_(x)PO₄/Cparticles at 300 to 750° C. for 2 to 12 hours, e.g., at 500 to 700° C.for 3 to 6 hours.

Another aspect of this disclosure relates to a mesoporous nano-compositeLiMn_(1-x)Fe_(x)PO₄ particle prepared by the above-described process.

Still within the scope of this disclosure is a mesoporous nano-compositeLiMn_(1-x)Fe_(x)PO₄ particle containing phospho-olivineLiMn_(1-x)Fe_(x)PO₄ crystals and a uniform carbon coating on the surfaceof the particles. The particle has a particle size of 10 to 100 nm(e.g., 50-80 nm), a surface area of 30 to 50 m²g⁻¹ (e.g., 40 to 50m²g⁻¹), and a pore size of 3 to 40 nm (e.g., 3 to 30 nm). The carboncoating has an average thickness of 1 to 10 nm (e.g., 3 to 7 nm).

The details of one or more embodiments of the disclosure are set forthin the description below. Other features, objects, and advantages of theinvention will be apparent from the description and the claims.

DETAILED DESCRIPTION

This disclosure provides a cost effective process for preparingmesoporous nano-composite LiMn_(1-x)Fe_(x)PO₄ (0≦x≦1) particlesemploying easy scalable soft-template synthesis followed by simplere-engineering.

The process includes steps (a) to (e). See the Summary section above.Each step is described in detail below.

Step (a)

A mixture is provided in this first step of soft-template synthesis ofthe mesoporous nano-composite LiMn_(1-x)Fe_(x)PO₄ particles. The mixtureincludes a soft-template compound, a lithium ion-containing compound, aniron ion-containing compound, a manganese ion-containing compound, aphosphate ion-containing compound, and a solvent at a predeterminedweight ratio.

The mixture can be a solution or a slurry. Preferably, it is a solutionin which these compounds are dissolved in the solvent. When the mixtureis a slurry, the compounds are dispersed in the solvent and mixed wellwith each other. It is preferred that the compounds are at astoichiometric molar ratio, e.g., Li:Mn:Fe:PO₄=1:(1-x):x:1.

The mixture is then stirred at a predetermined temperature (e.g., roomtemperature or an elevated temperature) for an adequate duration toallow formation of LiMn_(1-x)Fe_(x)PO₄ nanocrystals that are coated withthe soft-template compounds. Without being bound by any one theory, themechanism for forming the nanocrystals is described in Balaya et. al.,the International Patent Application Publication, WO 2012/023904.

The soft-template compound, usually a carbon-containing surfactant or acationic surfactant, is a compound that can self-assemble into micellesat its critical micellar concentration. These micelles can provide microor meso pores for the growth of LiMn_(1-x)Fe_(x)PO₄ nanocrystals and canalso restrict them from overgrowth. The soft-template compound can be asurfactant for providing suitable micelle morphology and size forgrowing LiMn_(1-x)Fe_(x)PO₄ nanocrystals. Examples include, but are notlimited to, (1-dodecyl)trimethylammonium bromide,(1-hexadecyl)trimethylammonium bromide, octadecyltrimethylammoniumbromide, tetradecyltrimethylammonium bromide, decyltrimethylammoniumbromide, octyltrimethyl ammonium bromide, trimethyloctadecylammoniumchloride, docosyltrimethylammonium chloride, pluronic P-123, pluronicF127, pluronic F 68, and a combination thereof. The concentration of thesoft-template compound in the solvent is 0.001 to 0.2 mol/L (e.g., 0.005to 0.15 mol/L) . The weight ratio of the soft-template compound to thelithium ion-containing compound described below is 1:1 to 10:1 (e.g.,6:1).

The lithium ion-containing compound, the iron ion-containing compound,the manganese ion-containing compound, and the phosphate ion-containingcompound are the sources for the lithium ions, the iron ions, themanganese ions, and the phosphate ions that form the LiMn_(1-x)Fe_(x)PO₄nanocrystals. These compounds can be provided in a powder or particulateform. Hydrates of these compounds, if available, can also be used. Thesematerials are well known in the field of chemistry.

The lithium ion-containing compound can be an ionic compound of lithium,e.g., an organic lithium salt, an inorganic lithium salt, and lithiumhydroxide. Examples include, but are not limited to, lithium fluoride,lithium chloride, lithium bromide, lithium iodide, lithium nitrate,lithium nitrite, lithium sulfate, lithium hydrogen sulfate, lithiumsulfite, lithium bisulfite, lithium carbonate, lithium bicarbonate,lithium borate, lithium phosphate, lithium dihydrogen phosphate, lithiumhydrogen ammonium phosphate, lithium dihydrogen ammonium phosphate,lithium silicate, lithium antimonate, lithium arsenate, lithiumgenninate, lithium oxide, lithium salts with carboxylic acids (e.g.,acetate and oxalate) or hydroxyl carboxylic acids (e.g., glycolate,lactate, citrate, and tartrate), lithium alkoxide, lithium enolate,lithium phenoxide, lithium hydroxide, and a combination thereof.

The iron ion-containing compound and the manganese ion-containingcompound can be is ionic compounds, e.g., organic and inorganic salts.Examples include, but are not limited to, iron and manganese fluorides,chlorides, bromides, iodides, acetyl acetonates, nitrates, nitrites,sulfates, hydrogen sulfates, sulfites, bisulfites, carbonates,bicarbonates, borates, phosphates, hydrogen ammonium phosphates,dihydrogen ammonium phosphates, oxide bis(2,4-pentanadionate), sulfateoxides, silicates, antimonates, arsenates, germanates, oxides,hydroxides, carboxylates, alkoxides, enolates, phenoxides, and acombination thereof. Note that each of the iron and manganese ions inthese compounds may have an oxidation state that is different from thatfound in the LiMn_(1-x)Fe_(x)PO₄ product. Oxidizing or reducingconditions can be applied to bring the oxidation state of the startingions to that found in the final product. For example, the soft-templatereaction can be carried out in a reducing atmosphere such as hydrogen,ammonia, and methane. See Balaya et al., WO 2012/023904 A1.

Examples of the phosphate ion-containing compound include, but are notlimited to, alkali metal phosphates, alkaline metal phosphates,transition metal phosphates, and non-metal phosphates (e.g., phosphoricacid, ammonium dihydrogen phosphate, ammonium hydrogen phosphate, andammonium phosphate), and a combination thereof. A compound containingtwo or more of lithium, iron, manganese, and phosphate ions can be used.For example, lithium dihydrogen phosphate can be used to provide bothlithium ions and phosphate ions.

The solvent can be an inorganic or organic solvent. Examples include,but are not limited to, water, methanol, ethanol, propanol, butanol,hexanol, or a combination thereof. A preferred solvent is a mixture ofethanol and water.

Turning back to the mixture, it can be stirred to allow completedissolution or homogeneous dispersion of the compounds.LiMn_(1-x)Fe_(x)PO₄ nanocrystals may be formed in and precipitated fromthe mixture during the stirring.

Step (b)

The solvent is removed (e.g., by evaporation at an elevated temperature,by filtration, and by centrifuge) from the mixture to obtain aLiMn_(1-x)Fe_(x)PO₄ precursor. The LiMn_(1-x)Fe_(x)PO₄ precursorcontains LiMn_(1-x)Fe_(x)PO₄ nanocrystals, which are formed by stirringthe mixture of step (a) or by removing solvent in this step.

Step (c)

The LiMn_(1-x)Fe_(x)PO₄ precursor thus obtained is calcined to obtaincrystalline LiMn_(1-x)Fe_(x)PO₄ grains. The calcination is carried outat a high temperature (e.g., 550 to 750° C., 600 to 700° C., and 650°C.) for an adequate duration (e.g., 2 to 12 hours, 3 to 6 hours, and 4hours). The crystalline LiMn_(1-x)Fe_(x)PO₄ grains thus obtained havemesopores in nano sizes (e.g., 3-30 nm). The mesopores are formedbetween two or more adjacent LiMn_(1-x)Fe_(x)PO₄ nanocrystals. The sizesof the mesopores can be controlled by the calcination temperature andthe milling conditions, which will be described below. During thecalcination, the soft-template compound on the surface of thenanocrystals is decomposed to form a carbon coating in a thickness of 1to 10 nm (e.g., 2 to 5 nm).

Preferably, the above-described calcining step is conducted under anessentially non-oxidizing atmosphere, such as vacuum and inert gas(e.g., nitrogen, helium, and argon with or without hydrogen).

Step (d)

The crystalline LiMn_(1-x)Fe_(x)PO₄ grains are ball milled to obtainnanostructured LiMn_(1-x)Fe_(x)PO₄ particles. The ball milling speed(e.g., 300 to 600 rpm), time (e.g., 2 to 24 hours), and ball to grainweight ratio (e.g., 10:1 to 50 :1, preferably 20:1 to 40:1) areoptimized to afford the final nanoparticles in the size below 100 nm(e.g., 10 to 100 nm, preferably 50 to 80 nm).

It is preferred that the ball milling is conducted in the presence ofconductive carbon. The amount of the conductive carbon can be added tothe crystalline grains so that the nanoparticles after ball milling arecoated with conductive carbon in a thickness of 1 to 10 nm (e.g., 3 to 7nm). Examples of conductive carbon include, but are not limited to,acetylene black, conductive carbon black (e.g., Printex XE2, BlackPearls 2000, and Ketjenblack), carbon nanotubes (e.g., single-walledcarbon nanotubes and multi-walled carbon nanotubes), and graphiticnano-sheets.

Step (e)

After ball milling, the nanostructured LiMn_(1-x)Fe_(x)PO₄ particles areannealed to yield mesoporous nano-composite LiMn_(1-x)Fe_(x)PO₄particles. The annealing can be conducted at 300 to 750° C. (e.g.,500-700° C.) for 2 to 24 hours (e.g., 3 to 6 hours). Annealing removeslattice strains developed during the high energy milling and restorescrystallanity lost also during the milling is without affecting thecrystallite size (e.g., 50 to 80 nm). Lattice strains and crystallanityloss negatively affect the electroactivities of the LiMn_(1-x)Fe_(x)PO₄nanoparticles.

The mesoporous nano-composite LiMn_(1-x)Fe_(x)PO₄ particles thusobtained have a phospho-olivine crystal structure, a particle size of 10to 100 nm (e.g., 50 to 80 nm), a surface area of 30 to 50 m²g⁻¹ (e.g.,40 to 50 m²g⁻), and a pore size of 3 to 40 nm (e.g., 3 to 30 nm).

The above-described process provides (i) homogeneous mixing of thereactants thereby avoiding any non-stoichiometry, (ii) high degree ofcrystallinity, (iii) control over particle size and pore size, (iv)in-situ coating of conductive carbon onto the surface ofLiMn_(1-x)Fe_(x)PO₄ particles, (v) improved kinetics of ions andelectrons, (vi) strengthening of conductive carbon coated on the surfaceof the particles during reheating, (vii) reliving of the lattice straincreated during milling using reheating process, and (viii) opportunitiesto make a product more crystalline during annealing.

Furthermore, this process eliminates problems associated with inherentlypoor kinetics of LiMn_(1-x)Fe_(x)PO₄ materials made by other processessuch as solid phase synthesis. The ball milling and annealing steps ofthis process can enhance the lithium ionic diffusion, the electronicdiffusion, and the crystallanity of the mesoporous nano-compositeLiMn_(1-x)Fe_(x)PO₄ particles. In sum, the LiMn_(1-x)Fe_(x)PO₄/Cparticles prepared by this process offer increased energy storage andpower density, which are critical for hybrid and electric vehicles.

A person skilled in the art can determine without undue experimentationthe types and amounts of solvent, the lithium ion-containing compound,the manganese ion-containing compound, the iron ion-containing compound,and the phosphate ion-containing compound. The skilled artisan can alsodetermine other conditions, such as calcination temperature, millingspeed, ball to grain weight ratio, and annealing time.

The specific examples below are to be construed as merely illustrative,and not limitative of the remainder of the disclosure in any waywhatsoever. Without further elaboration, it is believed that one skilledin the art can, based on the description herein, utilize the presentinvention to its fullest extent. All publications cited herein areincorporated by reference in their entirety.

Example 1: Preparation of Mesoporous Nano-CompositeLiMn_(0.2)Fe_(0.8)PO₄ Particles

Mesoporous nano-composite LiMn_(0.2)Fe_(0.8)PO₄ particles weresynthesized using the easy scalable soft-template method followed byhigh energy ball milling with conductive carbon and mild annealing.First, (1-hexadecyl)trimethylammonium bromide (3.64 grams, used as asoft-template compound) was dissolved in a mixture of ethanol and water(120 milliliters, ethanol/water : 5/1 by volume). To the surfactantsolution were added lithium dihydrogen phosphate (0.6 grams, as an ionsource of both lithium ions and phosphate ions), manganese acetatetetrahydrate (0.2828 grams, as a manganese ion-containing compound), andiron (II) acetate (0.8033 grams, as an iron ion-containing compound).The resulting mixture was stirred at ambient temperature for 12 hours.The solvent was removed using roto-evaporator at 80° C. to obtain aLiMn_(0.2)Fe_(0.8)PO₄ precursor. The precursor was calcined at 650° C.for 6 hours to yield crystalline LiMn_(0.2)Fe_(0.8)PO₄ grains. Thecrystalline grains, to which was added conductive carbon (0.15 to 0.5grams), were ball-milled at a rotary speed of 500 rpm for 4 hours. Afterball milling, the milled particles were annealed at 500 ° C. for 3 hoursto yield mesoporous nano-composite LiMn_(0.2)Fe_(0.8)PO₄ particles. Theannealing made the particles more crystalline and removed latticestrains developed during the high energy ball milling. The particlesthus obtained in general had a size of 50-80 nm.

Example 2: Preparation of Mesoporous Nano-CompositeLiMn_(0.5)Fe_(0.5)PO₄ Particles, LiMn_(0.8)Fe_(0.2)PO₄ Particles, andLiMnPO₄ Particles

Mesoporous nano-composite LiMn_(0.5)Fe_(0.5)PO₄ particles,LiMn_(0.8)Fe_(0.2)PO₄ particles, and LiMnPO₄ particles were synthesizedusing the same procedures as described in Example 1 except for theamounts of the reactants. The reactant weights are listed in Table 1below.

TABLE 1 The weights of the compounds used to synthesize mesoporousLiMn_(1-x)Fe_(x)PO₄ particles Water- Cationic ethanol, LiH₂PO₄ Mn(OAc)₂Fe(OAc)₂ surfactant 5:1, v/v LiMn_(1-x)Fe_(x)PO₄ grams grams grams gramsmL LiMn_(0.5)Fe_(0.5)PO₄ 0.6 0.7072 0.5020 3.64 120LiMn_(0.8)Fe_(0.2)PO₄ 0.6 1.1315 0.2008 3.64 120 LiMnPO₄ 0.6 1.4144 —3.64 120

Example 3: Characterization of Mesoporous Nano-CompositeLiMn_(1-x)Fe_(x)PO₄ Particles

The particles were subjected to X-ray diffraction (“XRD”) structuralanalysis. The XRD patterns show a single crystal form (i.e.,orthorhombic structure) of the particles prepared in Examples 1 and 2.

Furthermore, images of these particles were taken using a field emissionscanning electron microscopy (FESEM) and a transmission electronmicroscopy (TEM). The surface area is and the pore size distributionwere measured using a BET and surface analyzer by performing N₂adsorption and desorption experiments. The particles were shown to havea particle size of 50-80 nm, a surface area of 35-50 m²g⁻¹, and a poresize of 3-27 nm.

Example 4: Electrochemical Performance of Mesoporous Nano-CompositeLiMn_(1-x)Fe_(x)PO₄ Particles

In order to estimate the lithium storage performance of theLiMn_(1-x)Fe_(x)PO₄ particles, cathodic electrodes were fabricated withthe active material, acetylene carbon black and binder (Kynar 2801) inthe weight ratio of 80:10:10, 75:15:10 or 65:25:10. N-methyl pyrrolidone(NMP) was used as the solvent. Cathodic electrodes which had a thicknessof 10 μm and a geometrical area of 2.01 cm² were prepared using anetched aluminum foil as the current collector. Coin-type cells (size2016) were assembled in an Argon-filled glove box, using each of theabove-described cathodic electrodes, a lithium metal foil as thenegative electrode, 1 mol/L LiPF₆ in the mixture of ethylene carbonateand diethyl carbonate (1:1, v/v) or a mixture of ethylene carbonate anddimethyl carbonate (1:1, v/v) as the electrolyte, and a Whatman glassmicrofiber filter (Grade GF/F) or a Celgard 2502 membrane as theseparator. The cells were aged for 12 hours before a test.Charge-discharge cycling at a constant current was carried out using abattery tester.

The cells were cycled at different current densities, i.e., 0.05C, 0.1C,0.2C, 0.5C, 1C, 2C, 5C, 10C, 20C, and 30C, in which 1C relates toextracting 170 mAg⁻¹ in an hour. The cells demonstrated unexpectedlystable storage capacity as shown in Table 2. For example,LiMn_(0.5)Fe_(0.5)PO₄ cells achieved a storage capacity of 157 mAh g⁻¹at 0.1C and 45 mAh g⁻¹ at 30C.

The cells also demonstrated unexpectedly high energy density, which isshown in

Table 3. For examples, the observed energy density ofLiMn_(0.2)Fe_(0.8)PO₄ particles, LiMn_(0.5)Fe_(0.5)PO₄ particles, andLiMn_(0.8)Fe_(0.2)PO₄ particles all exceeded the theoretical values forLiCoO₂ (the most widely used cathodic material for lithium ionbatteries) and LiFePO₄ (a promising substitute for LiCoO₂).

TABLE 2 Storage performance of mesoporous nano-compositeLiMn_(1-x)Fe_(x)PO₄/C particles C rates 0.05 C 0.1 C 0.2 C 0.5 C 1 C 2 C5 C 10 C 20 C 30 C Mesoporous Storage performance ofLiMn_(1-x)Fe_(x)PO₄/C nano-composite (x = 0, 0.2, 0.5 and 0.8) mAh · g⁻¹LiMn_(0.2)Fe_(0.8)PO₄ 168 155 146 134 128 115 94 72 48 40LiMn_(0.5)Fe_(0.5)PO₄ — 157 155 145 134 123 100 83 52 45LiMn_(0.8)Fe_(0.2)PO₄ — 162 158 154 147 129 108 88 50 44 LiMnPO₄ 140 12097 95 61 41 20 — — —

TABLE 3 Specific energy of LiMn_(1-x)Fe_(x)PO₄, LiFePO₄ and LiCoO₂Specific energy, Wh · kg⁻¹ Mesoporous nano- Theoretical Observedcomposite materials specific energy specific energyLiMn_(0.2)Fe_(0.8)PO₄/C 609 666 at 0.05 C, 554 at 0.1 CLiMn_(0.5)Fe_(0.5)PO₄/C 643 592 at 0.1 C LiMn_(0.8)Fe_(0.2)PO₄/C 678 643at 0.1 C LiMnPO₄/C 701 574 at 0.05 C, 492 at 0.1 C LiFePO₄/C 586 Notmeasured LiCoO₂/C 561 Not measured

In addition, the cells were subject to galvanostatic charge-dischargecycling tests. The results of these tests showed that the high potentialand the flat potential vs. Li/Li+ occurred at about 4.1 V and 3.45 V,respectively, which represented a gain of 0.6-0.7 V at the highpotential compared to LiFePO₄/C cathode material.

Other Embodiments

All of the features disclosed in this specification may be combined inany combination. Each feature disclosed in this specification may bereplaced by an alternative feature serving the same, equivalent, orsimilar purpose. Thus, unless expressly stated otherwise, each featuredisclosed is only an example of a generic series of equivalent orsimilar features. is From the above description, one skilled in the artcan easily ascertain the essential characteristics of the presentinvention, and without departing from the spirit and scope thereof, canmake various changes and modifications of the invention to adapt it tovarious usages and conditions. Thus, other embodiments are also withinthe claims.

1. A mesoporous nano-composite particle, comprising: phospho-olivineLiMn_(1-x)Fe_(x)PO₄ crystals forming a grain, in which 0≦x≦1, and auniform carbon coating on the surface of the grain, the coating havingan average thickness of 1 to 10 nm, wherein the particle has a particlesize of 10 to 100 nm, a surface area of 30 to 50 m²g⁻¹, and a pore sizeof 3 to 40 nm.
 2. The particle of claim 1, wherein the particle has aparticle size of 50 to 80 nm, a surface area of 40 to 50 m²g¹, and apore size of 3 to 30 nm, and the carbon coating has an average thicknessof 3 to 7 nm.
 3. The particle of claim 1, wherein the carbon coating isformed of conductive carbon selected from the group consisting ofacetylene black, conductive carbon black, carbon nanotubes, andgraphitic nano-sheets.
 4. The particle of claim 3, wherein theconductive carbon is conductive carbon black selected from the groupconsisting of Printex XE2, Black Pearls 2000, and Ketjenblack.
 5. Theparticle of claim 2, wherein the carbon coating is formed of conductivecarbon selected from the group consisting of acetylene black, conductivecarbon black, carbon nanotubes, and graphitic nano-sheets.
 6. Theparticle of claim 5, wherein the conductive carbon is conductive carbonblack selected from the group consisting of Printex XE2, Black Pearls2000, and Ketjenblack.
 7. The particle of claim 1, wherein x is 0, 0.2,0.5, or 0.8.
 8. The particle of claim 7, wherein the particle has aparticle size of 50 to 80 nm, a surface area of 40 to 50 m²g⁻¹, and apore size of 3 to 30 nm, and the carbon coating has an average thicknessof 3 to 7 nm.
 9. The particle of claim 7, wherein the carbon coating isformed of conductive carbon selected from the group consisting ofacetylene black, conductive carbon black, carbon nanotubes, andgraphitic nano-sheets.
 10. The particle of claim 1, wherein 0<x<1. 11.The particle of claim 10, wherein the particle has a particle size of 50to 80 nm, a surface area of 40 to 50 m²g⁻¹, and a pore size of 3 to 30nm, and the carbon coating has an average thickness of 3 to 7 nm. 12.The particle of claim 10, wherein the carbon coating is formed ofconductive carbon selected from the group consisting of acetylene black,conductive carbon black, carbon nanotubes, and graphitic nano-sheets.13. The particle of claim 12, wherein the conductive carbon isconductive carbon black selected from the group consisting of PrintexXE2, Black Pearls 2000, and Ketjenblack.
 14. The particle of claim 11,wherein the carbon coating is formed of conductive carbon selected fromthe group consisting of acetylene black, conductive carbon black, carbonnanotubes, and graphitic nano-sheets.
 15. The particle of claim 14,wherein the conductive carbon is conductive carbon black selected fromthe group consisting of Printex XE2, Black Pearls 2000, and Ketjenblack.16. The particle of claim 10, wherein x is 0.2, 0.5, or 0.8.
 17. Theparticle of claim 16, wherein the particle has a particle size of 50 to80 nm, a surface area of 40 to 50 m²g⁻¹, and a pore size of 3 to 30 nm,and the carbon coating has an average thickness of 3 to 7 nm.
 18. Theparticle of claim 16, wherein the carbon coating is formed of conductivecarbon selected from the group consisting of acetylene black, conductivecarbon black, carbon nanotubes, and graphitic nano-sheets.
 19. Theparticle of claim 18, wherein the conductive carbon is conductive carbonblack selected from the group consisting of Printex XE2, Black Pearls2000, and Ketjenblack.
 20. A mesoporous nano-compositeLiMn_(1-x)Fe_(x)PO₄particle, wherein the particle is prepared by aprocess including the following steps: providing a solvent containing asoft-template compound, a lithium ion-containing compound, an ironion-containing compound, a manganese ion-containing compound, and aphosphate ion-containing compound; removing the solvent to obtain aLiMn_(1-x)Fe_(x)PO₄ precursor; calcining the LiMn_(1-x)Fe_(x)PO₄precursor to obtain crystalline LiMn_(1-x)Fe_(x)PO₄ grains; milling thecrystalline LiMn_(1-x)Fe_(x)PO₄ grains in the presence of conductivecarbon to obtain nanostructured LiMn_(1-x)Fe_(x)PO₄/C particles; andannealing the nanostructured LiMn_(1-x)Fe_(x)PO₄/C particles to obtainnano-composite LiMn_(1-x)Fe_(x)PO₄/C particles, wherein the amounts ofthe lithium ion-containing compound, the ferrous ion-containingcompound, the manganese ion-containing compound, and the phosphateion-containing compound are in stoichiometric proportion; and the weightratio of the soft-template compound to the lithium ion-containingcompound is 1:1 to 10:1.